In article <32999993.7DE1@hks.se>, Niklas.Nikitin@hks.se says...

>Which one of three followin Nikkor lenses should I choose:
>* 20/3.5 AI US$ 450, Second hand in good shape
>* 20/2.8 AIS US$ 600, Second hand in good shape
>* 20/2.8 AFD US$ 750, Demo product (almost new)
>Please send me any comment regarding there optical/mecanical qualites.
>Or any other tip about which one to choose!

Hmmm, you carry my "SUBJECTIVE Lens Evaluations (Mostly Nikkors)"
on your web page, and you still ask this...?! ;-)
Nikon has made a VERY few relatively poor lenses, and the compact
20mm f4 and f3.5 made previous to the excellent current f2.8's are
two, eliminating the first choice...
The second two are the same optically, but the feel is quite
different (though the AF 20mm has a better feel than many AF lenses).
I would go with the better feel and lower price of the AIS, unless
the AF and D features are important to you (they sure aren't to me!).
I would also get a return agreement and check the lens - all four
corners should be sharp by f5.6 on slides on good samples (the 20mm
f2.8 samples vary slightly, poorer ones require f8 to sharpen the
far corners).
Hope This Helps